The Boston Celtics defeated the Brooklyn Nets 115-114 on Sunday in the first game of their first-round playoff series.
After a Boston possession in the frantic final seconds, Tatum scored 16 of his 31 points in the second half. Jaylen Brown dribbled toward the middle and swung the ball out to Smart, who fired it in to a cutting Tatum, who spun around and dropped in his layup just before time expired.
For the longest streak in Celtics history, Tatum has four straight 30-point games in the playoffs, matching Larry Bird's streak in 1987. His buzzer-beater was the first for the Celtics in the playoffs since 2010 against the Miami Heat.
Brown had 23 points. Horford and Smart both had 20 points and four 3-pointers.
Irving had 18 points in the fourth quarter. The Celtics forced the ball out of his hands the last time Brooklyn had it, and Kevin Durant missed a jumper with a one-point lead that set up the Celtics final possession.
He added 23 points, but shot just 9-of-24.
Boston charged out of halftime with a 23-8 run to open a 82-69 lead, sparked by Smart's dead-eye shooting from beyond thearc.
The Celtics seemed to change their approach to guarding Durant in the half court, fronting him and sending help over the top to limit his driving ability.
They had to exert more energy to get off their attempts at scoring.
It did not last.
With Boston leading early in the fourth, Irving got Brooklyn back in the game with two straight 3-pointers and a layup to trim Boston's advantage to 98-97 with just over 9 minutes left. Then, following an empty trip by Boston that saw Horford and Brown fail to convert from in close, Durant calmly drained a 3 on the other end to put the Nets in front.
Brooklyn had increased its lead to a point where it was in danger of being overtaken by the other team. Brown connected on a 3 from the wing after finding space on the Celtics next possession. The Nets turned it over after a foul was called. Smart slid underneath Irving and tied it with a layup.
With less than 2 minutes left in the game, the score was tied again at109 and Brooklyn had a chance to take the lead. Horford's follow shot tied it again. The Nets had a 114-111 cushion when Irving came down the floor.
Brown made a layup out of a timeout.
During the pre-game introductions, Irving received the loudest jeers and was booed when he touched the ball the rest of the way.
Bruce Brown made headlines last week after suggesting Celtics big men Horford and Daniel Theis might be easy to attack inside without Robert Williams III available to defend the rim.
Horford played the opening 12 minutes as if he was going to destroy that idea.
Boston entered the game with the best defensive rating since the All-Star break and applied early pressure. He tried to establish himself in the post in the first quarter, but the Celtics stripped him three times.
Brooklyn had seven turnovers in the quarter and Boston had a 29-28 lead.
Horford was active throughout, going 3-for-4 from the field with 10 points.
Theis picked up his third foul and Boston had to adjust. When he was whistled for his fourth foul with 4:58 left in the period, things evened out.
The Celtics went on a 9-2 run before the Nets came back to tie the game at 61 at the half.
Information and The Associated Press contributed to the report.